There is a known fine particle sorting device (e.g., flow cytometer) that optically, electrically, or magnetically detects a characteristic of a fine particle of a cell or the like, and sorts and collects only a fine particle having a predetermined characteristic.
During cell sorting by the flow cytometer, a fluid stream (laminar flow including sample liquid including a cell, and sheath liquid) is firstly generated from an orifice formed in a flow cell, vibration is applied to the orifice so as to form a droplet from the fluid stream, and electric charge is applied to the droplet. Then, a moving direction of the droplet including the cell discharged from the orifice is electrically controlled, and a target cell having a desired characteristic and a non-target cell other than the mentioned cell are collected in different collection containers.
For example, Patent Document 1 discloses, as a microchip type flow cytometer, “a fine particle sorting device including: a microchip provided with a flow path through which liquid including a fine particle is made to flow, and an orifice to eject the liquid flowing through the flow path; a vibration element to form a droplet from the liquid at the orifice and discharge the droplet; charging means to apply electric charge to the discharged droplet; optical detection means to detect an optical characteristic of a fine particle flowing through the flow path; a pair of electrodes facing each other interposing the moving droplet and disposed along a moving direction of the droplet discharged to a space outside the chip; and two or more containers to collect droplets having passed between the pair of electrodes”.
Additionally, Patent Document 2 discloses a method of controlling operation of a flow cytometer capable of confirming whether a droplet is sorted to an intended flow path by arranging an auxiliary light and a detection unit at a position where the droplet breaks off from fluid. Since the break-off point is thus grasped, a delay time from when a fine particle of a cell or the like is detected until the droplet including the cell or the like reaches the break-off point can be grasped, and electric charge can be applied to the droplet containing a minute particle detected on the basis of the delay time.